1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a method and apparatus for supporting a Discontinuous Reception (DRX) operation in a mobile communication system.
2. Description of the Related Art
In general, mobile communication systems have been developed with an aim to provide communication while guaranteeing mobility of users thereof. With the rapid progress of technologies, such mobile communication systems have been developed to provide not only voice communication services but also high-speed data communication services. Now, the next-generation mobile communication system is being conducted to provide Human-to-Machine (H2M) communication and Machine-to-Machine (M2M) communication, beyond Human-to-Human (H2H) communication. In order to meet such a requirement, the 3rd Generation Partnership Project (3GPP), which is responsible for the standardization of communication, is working on a standard for machine-type communication. 3GPP SA1 Working Group (WG), which is responsible for defining services and characteristics thereof, is already discussing service requirements for machine-type communication.
FIG. 1 is a block diagram illustrating a communication scenario for machine-type communication according to the related art.
Referring to FIG. 1, machine-type communication devices 105 are connected with a wireless provider network 110. Generally, the machine-type communication devices 105 may be defined as various unattended devices, including as meters, automatic vending machines, and the like. The machine-type communication devices 105 may have characteristics different from those of the existing wireless User Equipments (UEs) in several respects. Also, the machine-type communication devices 105 may have different characteristics depending on the types thereof. One cell may include numerous machine-type communication devices 105. A machine-type communication server 115, which has information on the machine-type communication devices 105, functions not only to perform authentication, but also to gather and deliver information, which is collected from the machine-type communication devices 105. The machine-type communication server 115 delivers the information to a machine-type communication user 120. The machine-type communication server 115 may exist inside or outside of the wireless provider network 110. In addition, the machine-type communication user 120 is a final user who needs information delivered from the machine-type communication devices 105.
The machine-type communication has characteristics different from those of the existing wireless communication. Also, the characteristics of the machine-type communication are classified in various ways depending on the use purposes. For example, machine-type communication devices requiring communication only a few times a day regardless of time have a time-tolerant characteristic; and machine-type communication devices, which are installed at fixed positions without mobility and are configured to collect and transmit specific information, have a low mobility characteristic. Wireless providers have to provide services by taking characteristics of such various machine-type communications and the coexistence of machine-type communication devices and the existing UEs into consideration.
Of machine-type communication devices, tracking-related devices, such as devices equipped on animals or trucks, generally either use batteries, or are supplied with power generated by themselves. Therefore, because such machine-type communication devices can use only limited power, the machine-type communication services must be configured to efficiently use extremely small power. The 3GPP SA1 WG defines an extra low power consumption mode, in which machine-type communication devices may be set to use low power.
In the extra low power consumption mode, operations capable of reducing the use of power can be performed, wherein one of such operations is a method of lengthening a Discontinuous Reception (DRX) cycle. A UE performs a reception operation in order to receive a paging signal from an evolved Node B (eNB). However, a paging signal is not a frequently transmitted signal. Consequently, if the UE performs a reception operation even while the eNB does not transmit a paging signal, power loss becomes large. Therefore, in order to reduce power consumption, it is possible to periodically perform a reception operation only during specific time intervals so as to attempt to receive a paging signal, which is called a Discontinuous Reception (DRX). In a Long Term Evolution (LTE) system, the DRX operations of UEs being in an idle state are achieved by Equation 1 below. A System Frame Number (SFN) increases by one every radio frame. In a radio frame satisfying Equation 1 below, a paging signal is delivered, and a UE performs a reception operation based on DRX.SFN mod T=(T div N)*(U_ID mod N)  (1)
In Equation 1, “SFN” has 10 bits (i.e., MSB 8 bits explicit, and LBS 2 bits implicit), and “T” denotes a DRX cycle of a UE. The “T” is a value, which is included in a System Information Block Type 2 (SIB2) and is provided from an eNB, and may be, for example, rf32, rf64, rf128, or rf256. Also, “N” is “min (T, nB),” wherein “nB” is a value which is included in the SIB2 and is provided from the eNB, and may be, for example, 4T, 2T, T, T/2, T/4, T/8, T/16, or T/32. In addition, “UE_ID” is International Mobile Station Identity (IMSI) mod 1024, and 8 bits of a Master Information Block (MIB) of a Physical Broadcast CHannel (PBCH) represent an SFN.
FIG. 2 is a view showing a conception of a paging occasion in a conventional LTE technology according to the related art.
Referring to FIG. 2, an SFN increases by one every radio frame (see reference numeral 205). The SFN has a cycle of 1024, and is set to zero (see reference numeral 210). In addition, based on equation 1, a paging signal having the same pattern is repeated every SFN cycle (see reference numeral 215).
Most UEs corresponding to machine-type communication devices are expected to less frequently receive a paging signal than general UEs. For example, tracking-related devices will communicate with an eNB only a few times a day. Therefore, when a DRX cycle is set to be very long, it is possible to remarkably reduce power consumption due to reception operations. However, due to the characteristics of the 3GPP LTE system, the DRX cycle is limited by the length of an SFN. When the length of an SFN is 1024, the DRX cycle cannot exceed 1024. Accordingly, it is necessary to develop a method for first extending the length of an SFN in order to extend a DRX cycle, and a method for allowing an SFN extended for machine-type communication not to exert an influence on the paging operations of the existing UEs.
Therefore, a need exists for a method and apparatus for a Discontinuous Reception (DRX) operation in a mobile communication system. A need also exists for a method and apparatus for implementing a long SFN to extend the DRX cycle of a machine-type communication device in a mobile communication system.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.